Image Forming Apparatus

This application is based on and claims the benefit of priority from Japanese Patent Application No. 2024-179905 filed on October 15, 2024, the contents of which are hereby incorporated by reference.

The present disclosure relates to electrophotographic type image forming apparatuses such as copiers, printers, facsimile machines, and multifunction peripherals having their functions integrated together.

Conventional image forming apparatuses include an image forming portion and a sheet feed unit. The image forming portion forms an image on a recording medium. The sheet feed unit feeds the recording medium to the image forming portion. The sheet feed unit has a pickup rocker, a feed roller, and a retard roller. The pickup roller makes contact with the recording medium stored in a sheet feed cassette and feeds out the recording medium. The feed roller conveys the recording medium fed out by the pickup roller. The retard roller is kept in pressed contact with the feed roller to form a nip portion and conveys the recording medium while separating one sheet of it from the rest.

Downstream of the retard roller, a charge elimination member is arranged in a sheet conveyance passage. Thus, the recording medium electrostatically charged when passing through the retard roller has the electric charge on it eliminated by making contact with the charge elimination member. This makes it easy for the recording medium to peel off the retard roller and this helps reduce sheet feed failure.

In conventional image forming apparatuses, when the recording medium is fed at high speed, or the material of the retard roller is changed, or the type of recording medium is changed, the amount of charge on the recording medium may increase due to friction with the retard roller. In that case, the charge current flowing from the charge elimination member arranged in the sheet conveyance passage to the ground increases, so the supply voltage level in the apparatus may vary. This may lead to operation failure of circuit boards and sensors arranged near the sheet conveyance passage.

An object of the present disclosure is to provide an image forming apparatus that can reduce sheet feed failure while preventing operation failure.

To achieve the above object, according to one aspect of the present disclosure, an image forming apparatus includes an image forming portion and a sheet feed unit. The image forming portion forms an image on a recording medium. The sheet feed unit feeds the recording medium to the image forming portion. The sheet feed unit has a pickup roller, a feed roller, and a retard roller. The pickup roller makes contact with a recording medium stored in a sheet feed cassette and feeds out the recording medium. The feed roller conveys the recording medium fed out by the pickup roller. The retard roller is kept in pressed contact with the feed roller to form a nip portion and conveys the recording medium while separating one sheet of it from the rest. The feed roller is covered at least partly from above by a first charge elimination member. The first charge elimination member is grounded.

This and other objects of the present disclosure, and the specific benefits obtained according to the present disclosure, will become apparent from the description of embodiments which follows.

1 FIG. 1 FIG. 1 FIG. 100 100 1 2 1- 2 100 1 2 100 1 2 1 2 1 2 1 2 100 1 2 63 100 a An embodiment of the present disclosure will be described with reference to the drawings.is a sectional view showing the internal structure of an image forming apparatusaccording to a first embodiment of the present disclosure. For convenience’ sake, the vertical direction in an installed state (the state shown in) in which the image forming apparatusis ready for use is defined as the up-down direction (Z-Z). The front-rear direction (YY) is defined with the near-side face of the image forming apparatusin the plane of inas the front face. The left-right direction (X-X) is defined with respect to the front face of the image forming apparatusin the installed state. In this embodiment, the left-right direction (X-X) is orthogonal to the up-down direction (Z-Z) and to the front-rear direction (Y-Y). The left-right direction (X-X) is taken as the facing direction in which a pair of side faces of the image forming apparatusface each other and the front-rear direction (Y-Y) is taken as the axial direction of a feed roller. Note that the definition of the up-down direction is not meant to limit any directions or positional relationships as observed during the use of the image forming apparatus.

100 60 50 14 17 40 19 20 a d The image forming apparatusincludes image forming portions Pto P, a sheet feed unit, a transfer portion, a fixing portion, a discharge portion, a pair of conveyance rollers, a sheet conveyance passage, and a branch conveyance passage.

100 a b c d a d 1 FIG. In a main body of the image forming apparatus(here, a color printer), four image forming portions P, P, P, and Pare arranged in this order from upstream (the left side in) in the conveyance direction. The image forming portions Pto Pform images on a transfer sheet (recording medium) P.

a d a d More specifically, the image forming portions Pto Pare provided so as to correspond to images of four different colors (yellow, cyan, magenta, and black). The image forming portions Pto Pform yellow, cyan, magenta, and black images sequentially, each through the processes of electrostatic charging, exposure to light, image development, and image transfer.

a d a d a d a d a d 1 1 8 1 1 8 1 1 1 FIG. The image forming portions Pto Pform visible images (toner images) of the different colors on photosensitive drums (image carrying members)to. An intermediate transfer belt (intermediate transfer member)that rotates counterclockwise inis provided adjacent to the image forming portions Pto P. The toner images formed on the photosensitive drumstoare primarily transferred sequentially to, so as to be overlaid on each other on, the intermediate transfer belt, which moves while in contact with the photosensitive drumsto.

50 50 11 9 8 9 14 100 a d The transfer portiontransfers the toner images formed in the image forming portions Pto Pto the transfer sheet P (recording medium). The transfer portionhas a driving rollerand a secondary transfer roller. Specifically, the toner images primarily transferred to the intermediate transfer beltare secondarily transferred by the secondary transfer rollerto the transfer sheet P as one example of a recording medium. The transfer sheet P having the toner images secondarily transferred to it has the toner image fixed to it in the fixing portion, and is then discharged out of the main body of the image forming apparatus.

60 60 62 63 63 60 1 61 61 100 a d a b The sheet feed unitfeeds the transfer sheet P to the image forming portions Pto P. Specifically, the sheet feed unithas a pickup roller, a feed roller, and a retard roller. The sheet feed unitis arranged above Za sheet cassette. The sheet cassetteis arranged in a bottom part of the main body of the image forming apparatusand stores the transfer sheet P to which the toner images are to be secondarily transferred.

62 62 62 61 19 The pickup rolleris kept in pressed contact with the top face of the transfer sheet P with a predetermined pressure. Rotating the pickup rollerstarts the feeding of the transfer sheet P. That is, the pickup rollermakes contact with the transfer sheet (recording medium) P stored in the sheet cassetteand feeds out the transfer sheet (recording medium) P to the sheet conveyance passage.

63 63 63 63 62 63 63 a b a b a The feed rollerand the retard rollerconstitute a pair of feeding rollers. The feed rollerconveys the transfer sheet (recording medium) P fed out from the pickup roller. The retard rolleris kept in pressed contact with the feed rollerto form a nip portion and conveys the transfer sheet (recording medium) P while separating one sheet of it from the rest.

63 63 63 63 62 66 63 62 b a b a a 3 FIG. Specifically, the retard rolleris kept in pressed contact with and rotates by following the feed roller. The retard rollerincorporates a torque limiter. Between the feed rollerand the pickup rolleris arranged a driving force transmission gearthat transmits the rotation of the feed rollerto the pickup roller(see).

62 63 63 19 19 13 9 11 8 60 a b Thus, if a plurality of transfer sheets P are fed at the same time by the pickup roller, the feed rollerand the retard rollerseparate the transfer sheets P so as to pick out and feed only the topmost sheet to the sheet conveyance passage. The transfer sheet P having passed through the sheet conveyance passagereaches a pair of registration rollersand is conveyed to the nip portion between the secondary transfer rollerand the driving rollerof the intermediate transfer beltin time for image formation. The sheet feed unitwill be described in detail later.

8 25 8 9 Used as the intermediate transfer beltis a sheet of dielectric resin, which typically is a belt without a seam (seamless belt). A blade-form belt cleanerfor removing toner and the like remaining on the surface of the intermediate transfer beltis arranged downstream of the secondary transfer roller.

1 1 2 2 2 2 5 3 3 3 3 7 7 7 7 2 2 2 2 1 1 5 3 3 3 3 1 1 7 7 7 7 1 1 a d a b c d a b c d a b c d a b c d a d a b c d a d a b c d a d Around and below the photosensitive drumsto, which are rotatably arranged, there are provided charging devices,,, and, an exposure device, development devices,,, and, and cleaning devices,,, and. The charging devices,,, andelectrostatically charge the photosensitive drumsto. The exposure deviceshines light carrying image information onto the photosensitive drums 1a to 1d. The development devices,,, andform toner images on the photosensitive drumsto. The cleaning devices,,, andremove the developer (toner) and the like remaining on the photosensitive drumsto.

2 2 1 1 5 1 1 3 3 3 3 4 4 3 3 a d a d a d a d a d a d a d When image data is fed in from a host device such as a personal computer, first, the charging devicestoelectrostatically charge the surfaces of the photosensitive drumstouniformly. Next, the exposure deviceirradiates the photosensitive drumstowith light according to image data to form on them electrostatic latent images according to the image data. The development devicestoare loaded with predetermined amounts of two-component developer containing toner of different colors, namely yellow, cyan, magenta, and black respectively. When, as image formation proceeds and the proportion of the toner in the two-component developer in the development devicestofalls below a prescribed value, toner is supplied from toner containerstoto the development devicesto.

3 3 1 1 5 a d a d The toner in the developer is fed from the development devicestoto the photosensitive drumstoand electrostatically adheres to them. Thus, toner images are formed according to the electrostatic latent images formed by exposure to light from the exposure device.

6 6 6 6 1 1 1 1 8 1 1 7 7 a d a d a d a d a d a d Then, primary transfer rollerstoproduce electric fields at a predetermined transfer voltage between the primary transfer rollerstoand the photosensitive drumsto, and thereby the yellow, cyan, magenta, and black toner images on the photosensitive drumstoare primarily transferred to the intermediate transfer belt. These images are formed in a predetermined positional relationship. After that, in preparation for the subsequent formation of new electrostatic latent images, the toner and the like remaining on the surfaces of photosensitive drumstoafter primary transfer are removed by the cleaning devicesto.

8 10 11 11 8 13 11 9 8 The intermediate transfer beltis wound around a driven roller, arranged upstream, and the driving roller, arranged downstream. As the driving rolleris rotated by a belt driving motor (not illustrated), the intermediate transfer beltstarts rotating counterclockwise, and the transfer sheet P is conveyed with predetermined timing from the pair of registration rollersto a secondary transfer nip portion N between the driving rollerand the secondary transfer rollerprovided next to it. The toner images formed on the intermediate transfer beltare secondarily transferred to the transfer sheet P passing through the secondary transfer nip portion N.

14 14 14 14 14 14 14 14 a b a b a a The transfer sheet P having the toner images secondarily transferred to it is conveyed to the fixing portion. The fixing portionhas a fixing beltand a pressing roller. The fixing beltis heated with a heating device such as a heater or an induction heating portion (not illustrated). The pressing rolleris kept in pressed contact with the fixing beltto form a fixing nip and applies a rotational driving force to the fixing belt.

14 14 14 a b The transfer sheet P conveyed to the fixing portionis heated and pressed by the fixing beltand the pressing roller, so that the toner images are fixed to the surface of the transfer sheet P to form a predetermined full-color image.

40 15 19 20 18 17 The transfer sheet P with the full-color image formed on it is conveyed via the pair of conveyance rollersand then has its conveyance direction switched by a conveyance guide memberarranged in a branching portion of the sheet conveyance passageso as to be discharged as it is (or after being diverted to a branch conveyance passageto have images formed on both sides) to a discharge trayby a pair of discharge rollers (discharge portion).

40 14 17 The pair of conveyance rollersfeeds out the transfer sheet (recording medium) P from the fixing portionto the pair of discharge rollers (discharge portion).

19 60 50 14 17 20 19 40 19 13 20 1 2 102 100 The sheet conveyance passageconnects together the sheet feed unit, the transfer portion, the fixing portion, and the discharge portion. The branch conveyance passagebranches off the sheet conveyance passagedownstream of the pair of conveyance rollersand communicates with the sheet conveyance passageupstream of the pair of registration rollers. The branch conveyance passageextends in the up-down direction (Z-Z) along a side faceof the image forming apparatusand curves substantially in a C-shape.

2 FIG. 3 FIG. 3 FIG. 60 60 is a perspective view of a sheet feed unitandis an enlarged sectional part view of the sheet feed unit. In, the conveyance direction of the transfer sheet P is indicated by a dash-and-dot line.

60 69 62 63 63 60 19 60 100 71 72 69 a b The sheet feed unitfurther includes a housingthat holds the pickup roller, the feed roller, and the retard roller. The sheet feed unitconstitutes part of the conveyance face of sheet conveyance passage. The sheet feed unitis attachable to the apparatus main body of the image forming apparatusalong guide railsandarranged in the housing.

71 72 71 72 1 2 63 71 63 63 71 a a a The guide railsandare made of sheet metal and are electrically conductive. In this embodiment, the guide railsandextend parallel to the axial direction (Y-Y) of the feed roller. The guide railserves as a first charge elimination member and covers the feed rollerat least partly from above. That is, the feed rolleris covered at least partly from above by the guide rail (first charge elimination member).

71 63 a While, in this embodiment, the guide railis made of sheet metal, it can instead be a molding of resin as long as an electrically conductive member is arranged on its surface facing the feed roller.

71 100 63 63 71 63 63 71 19 19 19 a a a a The guide railis grounded to the ground via the main body frame of the image forming apparatus. As a result, the electric charge on the transfer sheet P electrostatically charged by friction with the feed rolleris eliminated via the feed rollerand the guide rail. This reduces the amount of charge on the transfer sheet P passing through the feed rollerand makes it easy for the transfer sheet P to peel off the feed roller. This helps reduce sheet feed failure. The guide rail (first charge elimination member)is arranged outside the sheet conveyance passageand the charge current passes via a position away from the sheet conveyance passage. This prevents malfunctioning of circuit boards and sensors arranged near the sheet conveyance passageand reduces operation failure in the apparatus.

71 60 60 The first charge elimination member is configured as the guide railand so, without increasing the number of the components of the sheet feed unit, it is possible to eliminate the charge on the transfer sheet P. It is thus possible to suppress an increase in the manufacturing cost of the sheet feed unit.

71 1 2 63 63 71 a a The guide railhas a length in the axial direction (Y-Y) greater than the axial length of the feed roller. Thus, the electric charge on the electrostatically charged transfer sheet P can be efficiently eliminated via the feed rollerand the guide rail.

63 71 63 71 a a In this embodiment, the feed rollerand the guide rail (first charge elimination member)face each other across a gap of 2.5 mm, and the gap is preferably 2 mm or more but 4 mm or less. If the gap is smaller than 2 mm, the feed rollerand the guide railmay come into contact with each other. If the gap is larger than 4 mm, the effect of charge elimination is low.

71 63 71 63 a a The guide rail (first charge elimination member)curves along the feed rollerto be convex outward in the radial direction. This makes it possible to secure a large region over which the guide rail (first charge elimination member)and the feed rollerface each other at an even distance in the radial direction. This helps enhance the effect of eliminating the charge.

4 FIG. 4 FIG. 1 3 FIGS.to 60 60 73 Next, a second embodiment of the present disclosure will be described.is an enlarged sectional part view of the sheet feed unitaccording to the second embodiment. In, the conveyance direction of the transfer sheet P is indicated by a dash-and-dot line. For convenience’ sake, the parts similar to those in the first embodiment described previously and shown inare identified by the same reference signs. In the second embodiment, the sheet feed unitfurther has a guide member. In other respects, the structure here is similar to that in the first embodiment.

73 19 62 71 73 62 63 The guide memberis arranged on the conveyance face of the sheet conveyance passagethat connects together the pickup rollerand the guide railand supports the bottom face of the transfer sheet (recording medium) P. Arranging the guide memberallow smooth conveyance of the transfer sheet (recording medium) P from the pickup rollerto the nip portion between the pair of feeding rollers. This helps further reduce sheet feed failure.

73 74 74 63 74 63 74 19 19 a a The top face of the guide memberis configured with a grounded second charge elimination member. The second charge elimination memberis, for example, made of electrically conductive sheet metal and stainless steel (SUS material) is suitably used. The electric charge on the transfer sheet P electrostatically charged by friction with the feed rolleris eliminated via the second charge elimination member. This further reduces the amount of charge on the transfer sheet P passing through the feed roller. Also, the charge current can be passed via the second charge elimination member, via a position away from the sheet conveyance passage. This prevents damage to circuit boards and sensors arranged near the sheet conveyance passageand reduces operation failure in the apparatus.

73 74 73 74 73 The guide memberand the second charge elimination membermay be configured as one integral member or may be configured as separate members. For example, the guide membermay be configured as a molding of resin and a plate-form second charge elimination membermay be arranged on the top face of the guide member.

74 1 2 63 63 1 2 74 a b The width of the second charge elimination memberin the axial direction (Y-Y) is greater than the width of the nip portion between the feed rollerand the retard rollerin the axial direction (Y-Y). Thus, the electric charge on the electrostatically charged transfer sheet P can be efficiently eliminated via the second charge elimination member.

74 100 74 100 74 71 The second charge elimination memberis grounded via the main body frame of the image forming apparatus. Specifically, the second charge elimination memberand the main body frame of the image forming apparatusare connected together via a wire spring, wire, conductive tape, or the like. The second charge elimination memberand the guide railmay be connected together via a wire spring, wire, conductive tape, or the like.

71 69 The present disclosure is not limited to the above embodiment and can be carried out with any modifications made without departure from the spirit of the present disclosure. For example, in the above embodiment, the first charge elimination member is configured as the guide rail; instead, a plate-form member of stainless steel (SUS material) may be arranged in the housingto serve as the first charge elimination member.

The present disclosure is applicable not only to color copiers but also to other vertical-conveyance type image forming apparatuses such as analog copiers, digital multifunction peripherals, monochrome and color printers, and facsimile machines.